So, obviously trying to rebuild a hulked battleship, and make yourself the big A on the block is a frequently voiced idea, and a rarely acted upon one, for numerous reasons, but while they haven't given us much of anything on battleships, minus stats for da Wurldbreaka and Kroot Spheres, would they be their own class? It might seem a dumb question, but I suppose it all comes down to a matter of size. Grand Cruisers and Battle Cruisers are each allowed to use "Cruiser class" parts, even though they are supposed to be somewhat bigger, and it is a rare component that actually says "bigger than cruisers only". Are Battleships truly still so much bigger that you'd need "Battleship components, or would cruiser bits do? In the event that only bigger is better, would there be any way to get them without every goober in the Expanse knowing? Even Winterscale doesn't have battleships, sometimes even Space marines limit themselves to more cruiser-scale vessels, and that means getting the parts for such an endeavor would be impossible quietly, only partly barring raiding every haunted Space Hulk you can find for hopeful "big ship" parts.
I suppose this might very well explain why such a thing hasn't occurred, but would it even be possible to get the parts, quietly or loudly, or should every wrecked battleship just be viewed as a cute joke, hopefully with an interior filled with loot worth pilfering? Lots of people have talked about rebuilding the Light of Terra, or some other vessel, but time and cost be damned, would the parts needed just still be unavailable? If I'm the Navy, and you want a battleship component, that must mean you have a battleship, and I don't want to have to fight it, someday, if you go from Rogue Trader to full-blown rogue. Why would I ever willingly sell it to you?